Full Paper 1-Pyrrolidine Dicarbodithioate Based Electrodes for Determination of Iron(III) in Lubrication Oil Mohsen M. Zareh,* Ismail F. A. Ismail, Mohamd H. Abd El-Aziz Department of Chemistry, Faculty of Science, Zagazig University, Zagazig 44519, Egypt *e-mail: mohsenzareh@hotmail.com, mmzareh@zu.edu.eg Received: November 12, 2009 Accepted: January 23, 2010 Abstract The lipophillic ammonium salt of 1-pyrrolidine dicarbodithioic acid (PCDT) (I) was introduced as a new selective ionophore for an iron selective electrode. In addition, the effect of immobilization of 18-crown-6 (18CE6) (membrane type-II), on the electrode performance was discussed. The slope of the PCDT-based (I) electrode was (20 mV/decade). The linear concentration range was (10 5 – 10 1 M) after one day doping. The detection limit for electrode type-(II) was (1.3  10 6 M). For membrane with only 18CE6 (type-III) the linear range and the detection limit were improved (10 5 – 10 1 M and 3.2  10 6 M, respectively). The pH-range was between 5 – 11 for type-II, and III electrodes, while it was 7 – 11 for type-I electrode. Most of the common cations were tested for the evaluation of the electrode selectivity with correlation to the ionic radii of the tested cations. Among them only Ag þ and Pb 2þ were the real interference for type-III electrode. Application of using the electrode for the determination of iron in lubrication oil samples was performed with RSD (1.77 – 2.7%) and (1.01 – 2.3%) for type-II and III electrodes, respectively. The corresponding recovery ranges were (93.0 – 99.9%) and (96.3 – 100%). The obtained results were compared to those of an atomic absorption spectrophotometric method. Keywords: Iron selective electrode, Dicarbodithioate based membrane, Analysis of lubrication oil, Ionophores, Immobilization DOI: 10.1002/elan.200900550 To the Spirit of Prof. Dr. I. F. A. Ismail, Who Died in September 2008. 1. Introduction The construction of ISEs, based on using neutral carriers, for either cations or anions was applied by Gopta and cow- orkers [1 – 6]. They prepared a lead ISE based on either diphenyltetrapyrazole and dipropoxycalix-4-arene deriva- tives [1], or based on tert-butylcalix-4-arene derivative [2]. In addition, they were synthesized iron and cobalt complexes of tetraazaporphyrin derivative and incorporated them into PVC matrix as ionophores to fabricate anion selective membrane electrodes which were responsive to azide and nitrite ions, respectively [3]. Uranyl ion selective electrode was applied based on tert-butylcalix-6-arene senor based membrane [5]. Poly(vinyl chloride) (PVC) based mem- branes of macrocycles, tetraazacyclotetradeca-4,11-diene diperchlorate derivatve(I), tetraazacyclo-tetradeca-4,11-di- ene diperchlorate derivative(II) and tetraphenylporphyr- in(III) were prepared and investigated as Co 2þ -selective electrodes [6]. Iron selective electrodes were found in the literature using different ionophores. Benzilthiocarbohydrazide [7] or N-(2- hydroxyethyl) ethylenediamine-N,N’,N’’-triacetic acid [8] were used as sensor materials for preparing a PVC (polyvinyl chloride) membrane ferric ISE by Zamani et al. They did not work in alkaline medium (pH range 1.5 – 4.5 and 1.8 – 4.5), although they had very sensitive linear ranges (10 2 – 10 7 and 10 2 – 10 9 M). Their life time was not more than 10 weeks. Benzo-18-crown-6 was applied as the sensor material for an iron III ion selective electrode by Ekmekci et al. [9]. The slope of that electrode was monovalent slope (57 mV/decade). The electrode was responding to FeCl  4 as an anion electrode. It had a life time extend to 2 months. An iron(III) ion-selective based on a m-bis-(tridentate) ligand (2-phenyl-1, 3-bis [3’-aza-4’-(2’-hydroxyphenyl)-prop-4-en- 1’-yl]-1, 3-imidazolidine) was constructed by Gupta et al. [10]. It had a working pH range 3.5 – 5.5. The age of this electrode was 2 months. Sil et al. [11] prepared a coated- wire iron(III) ion-selective electrode based on iron complex of 1,4,8,11-tetraazacyclotetradecane. The slope of that electrode was monovalent (60  5 mV/decade), with a pH working range 1.5 – 3.5. A novel ion selective potentiometric sensor for direct determination of Fe(III) in the presence of Fe(II) was constructed by Mashhadizadeh et al [12]. It was based on 2-[(2-hydroxy-1-propenyl-buta-1,3-dienylimino)- methyl]-4-p-tolylazo-phenol as a neutral carrier. It showed a super-Nernstian behavior (28.5 mV/decade) for at least 2 months. It works within pH range 4.5 – 6.5. Mahmoud [13] applied iron ion-selective electrodes for direct potentiom- etry and potentiotitrimetry in pharmaceuticals. The elec- trode was based on ion association complexes of iron(II) 2, Full Paper Electroanalysis 2010, 22, No. 12, 1369 – 1375  2010 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim 1369